MRTG uBR 10000

I have recently setup an MRTG system at work to monitor many, many devices. All is well with most all of the devices, however, the uBRs don't seem to wanna cooperate. All of the graphs for the cable interfaces have spikes in them. The spikes throw off the scale of the graphs quite a bit...to the point where they are nearly useless. Have any of you ever used a system like MRTG to monitor uBRs? If so, have you ever seen spikes in the graphs? If you did see spikes, what did you do to correct this?